Which word correctly completes this sentence? las invitadas en llegar a la fiesta fueron mis primas. 1.primero 2.primera 3.primeras 4.primeros

The key to figuring out the conjugation is looking at the gender of the definite article and whether it is singular or plural.

Las is plural and feminine, therefore, the following word must be plural and feminine.

3. primeras

B. la madre le lavó las manos